washington state vs the king county sewer capacity charge

One seemingly intractable cost to building a backyard cottage in Seattle has been the $10,000 king county sewer capacity charge levied against DADUs but not ADUs.   

Senate Bill 5812 is new legislation that is part of state wide effort intended to increase the amount of affordable rental housing by setting standards for both attached (ADUs) and detached accessory dwelling units (DADUs). If adopted the legislation will apply to all towns and cities with populations of greater than 2,500.  

One of the major costs of building DADUs have been capacity charges. In many municipalities capacity charges for a DADU are levied equal to those of a new single family residence.  The new legislation would require that utilities charge fees at a level that is proportionate to the actual cost of adding the service and additional consumption. This is particularly important for what might be considered more affordable DADUs, those that are smaller and in rural areas, as the existing cost per unit model represents a disproportionately large part of the budget for these units.  


For ADUs and DADUs the bill would also.

• Eliminate owner occupancy requirements
• Set a minimum size of 1,000 square feet
• Exclude garages from the maximum allowable size for DADUs.
• Eliminate parking requirements
• Allow one ADU and one DADU or two ADUs per primary residence

Comments can be submitted via link

Or via session Committee Assistant Elisabeth Weeks (elizabeth.weeks@leg.wa.gov)

And addressed to:

Madame Chair and Members of the Senate Housing Stability and Affordability
Committee,